Process and a device for even distribution and alternating supply of liquid and gaseous protective media for the refining gas tuyeres of a converter

ABSTRACT

An apparatus for insuring that the flow of a liquid or gaseous protecting fluid medium is uniform to a plurality of double tuyeres located in the lining of a refining vessel in which molten metal such as a pig iron is refined by a refining gas such as oxygen, introduced into the melt through double tuyeres. Means are also provided for shifting from a gas to a liquid or vice versa. The invention also includes the process of refining molten pig iron using such an apparatus.

United States Patent [191 Knuppel et al.

[ PROCESS AND A DEVICE FOR EVEN DISTRIBUTION AND ALTERNATING SUPPLYYOF LIQUID AND GASEOUS PROTECTIVE MEDIA FOR THE REFINING GAS TUYERES OF A CONVERTER [75] Inventors: Helmut Knuppel, Karl Brotzmann;

Hans Georg Fassbinder, all of SulzbachRosenberg, Germany [73] Assignee: Eisenwerk Gesellschaft,

Maximilianshutte M.B.H., Rosenberg, Germany 221 Filed: Dec. 8, 1972- 211 App1.No.: 313,308

[ 30] Foreign Application Priority Data Dec. 9, 1971- Germany 2161000 ['52] US. Cl. 75/60, 75/59 [51] Int. Cl C21c 5/34 [58] Field of Search, 4..., ..'75/60, 59

[ Dec. 3, 1974 '[56] References Cited UNITED STATES PATENTS 3,706,549 12/1972 Knuppel 75/60 FOREIGN PATENTS OR APPLICATIONS 1,113,201 11/1955 France 75/60 1,450,718 7/1966 France 75/60 Primary ExaminerL. Dewayne Rutledge Assistant ExaminerPeter D. Rosenberg Attorney, Agent, or Firm-Lawrence 1. Field '57 ABSTRACT An apparatus for insuring that the flow of a liquid or gaseous protecting fluid medium is uniform to a'plurality of double tuyeres located in the lining of a refining vessel in which molten metal such as a pig iron is refined by a refining gas such as oxygen, introduced into the melt through double tuyeres." Means are also provided for shifting from a gas to a liquid or vice versa. The invention also includes the process of refining molten pig iron using'such an apparatus.

8 Claims, 4 Drawing Figures PATENTEL 553 3 74 SHEET 10E 4 8 FIG PROCESS AND A DEVICE FOR EVEN DISTRIBUTION AND ALTERNATING SUPPLY OF LIQUID AND GASEOUS PROTECTIVE MEDIAFOR TIIE REFINING GAS TUYERES OF A CONVERTER The invention relates to a process wherein the converter tuyeres, which preferably consist of two concentric tubes and through the inner one of which passes a refining gas, especially oxygen, while a liquid or gaseous protecting'medium is made to pass through the annular space between the two tubes, are evenly and where necessary alternatingly loaded with the liquid and gaseous protecting medium.

Ordinarily, refining gas tuyeres in converters for the refining of metal melts, and preferably pig iron, are mounted in the refractory masonry underneath the bath surface. In recent years, a process for refining pig iron has been accepted in practice, wherein the concentric tubes tuyeres are made use of. This process is described in the German Auslegeschrift 1,583,968. The tuyeres are mounted in the bottoms of the ordinary Thomas converters that have been modified for the new steel refining process with oxygen and a protective medium. The protecting medium surrounding the oxygen jet prevents premature back-burning of the tuyeres and enhances the durability of the refractory lining. Liquid and/or gaseous hydrocarbons, for instance light fuel oil, propane or natural gas have been found particularly useful as protective media. In large-scale applications, several tuyeres areused simultaneously, and the number of tuyeres is in a definite relationship with the converter capacity. Thus a converter for refining steel melts with a capacity of I20 tons is provided with approximately l5 tuyeres.

When using liquidor gaseous hydrocarbons as the protecting medium, the quantity of protecting medium with respect to the quantity of oxygen is relatively small and for natural gas amounts to about 7 percent by volume and for propane to about 3 percent by volume.

However, differences in tuyere burn-offs are frequently observed in steel works operation. Closer examination of these initially inexplicable phenomena reveals that the flow rates of protective media through the tuyeres vary to a great extent. For example, it has been found that the actual propane rates varied from to 6 percent by volume with respect to oxygen at the individual tuyeres receiving the smaller amounts of propane burned back much faster and thus reduced the mean life of the converter bottom.

In contrast, oxygen distribution to the individual tuyeres causes no difficulties. Without any special control devices, oxygen is found to distribute evenly to all the tuyeres. Possibly the varying consumption of protective medium in the individual tuyeres is due to changes at the tuyere tips, due for instance to deposits or deformations. The clear flow cross-section for the protecting medium being much less than the cross-section of the oxygen tube, changes in the tuyere orifices provided for protective medium flow are appreciably more significant than for oxygen.

A process is also already known from the Offenlegungsschrift 2,033,975 wherein an even supply to each tuyere is achieved by means of a cooling substance. The pressure of the cooling liquid is regulated at eachtuyere and in this manner an even supply to the cially in the rough converter operation, this process suffers from drawbacks: either the entire regulating apparatus for increasing pressure and for flow-metering must bemounted directly at the tuyere end, that is, in a region jeopardized by heat and steel spatters, or else each tuyere must be provided with a separate supply which is difficult of execution because of converter tilting and especially disadvantageous in view of the expenditures with increasing numbers of tuyeres.

The present invention is directed to the provision of simple means for the even distribution of the protecting medium to the tuyeres. Furthermore; when an altemating operation with a liquid or a gaseous protective medium is contemplated a simple means to effect switching from liquid to gas or vice versa is required, without there being danger that appreciable amounts of liquid or gaseous protective media will mix.

In order to provide for such operation, in the present invention, the protective medium is subjected to a very high pressure at least twice that required for reliable operation at the entrance of the tuyere, the protective medium being in a supply line common to the tuyeres, and means are provided to reduce the pressure of the protective medium in the supply line, to that desired at the tuyere, e.g., by inserting throttles between the supply line and the tuyeres. The means for switching from liquid to gaseous protecting medium or vice versa are also located near the converter mantle in the region of the tuyeres.

Throttles suitable in the practice of the invention are those in which the pressure is decreased wholly or largely by acceleration of the protective medium. In the simplest case this is achieved by use of a diaphragm type throttle. However, other throttling systems exist,

which will be further described below. It is preferred to use throttles with as large clear cross-sections as possible, and having shapes which insure that impurities do not deposit on the throttle and hence alter the throt tling effect.

The invention will be made apparent from the description taken in conjunction with the drawings in which:

FIG. 1 is a view taken in section through a feed line for the protecting medium from the supply line to the tuyere, a diaphragm with the sharp edge in the flow direction being mounted in the feed line;

FIG. 2 is a view illustrating diagrammatically the principle of operation of a switching scheme for protective medium supply allowing switching from liquid to gaseous protective medium, or vice versa;

FIG. 3 is a section through a four way valve used in the apparatus of FIG. 2; and

FIG. 4 is a further embodiment of'a switching valve.

As best seen in FIG. 1, the apparatus comprised a diaphragm 4 with a sharp edge 5 facing in upstream direction is mounted in a feed line connecting the common protective fluid supply line 2 to tuyere 3'. The streamlines which are drawn-in dash lines show the operation of this diaphragm. The protecting medium flowing in the direction of the arrow contracts more than an amount corresponding to the clear, crosssection of the diaphragm opening given by diameter 6. The effective cross-section of this special diaphragm is therefore actually diameter 7.

If, for instance, the converter tuyeres are being supplied with 1,000 cubic meters/hour (standard temperature and pressure) of oxygen and if natural gas is being provided as the protective medium at a pressure atm. abs. in the supply line, and if the nominal flow rate of natural gas is 70 cubic meters/hour STP, then a diaphragm diameter of 3.8 mm must be used according to the invention, which will reduce the pressure of the natural gas supplied to the tuyere to approximately half of the nominal value indicated.

If, for instance, the pressure of the natural gas in the common supply line 2 amounts to atm. abs., then the indicated nominal flow rate of 70 m3/hour STP requires a diaphragm diameter of 2.7 mm.

The above mentioned examples indicate that as the pressure in the common supply line 2 for the tuyeres increases, the diaphragm diameters decrease. High pressure in the supply line is desirable because of the feasibility of considerable pressure reductions in the throttling means so that even marked pressure loss fluctuations in the tuyeres will only slightly affect the nominal flow rates.

However, the small diaphragm diameters required for high pressures suffer from the drawback of increasing danger of clogging. This is particularly true when hydrocarbon gases are being used as protective media. At high temperatures, the danger increases that the hydrocarbons will crack and that soot will occur along with other products, which again may lead to clogging of small diaphragms. Installation of special throttling means permitting larger free cross-sections as compared with conventional diaphragms (for the same pressure reduction) results in improved operations. Such throttling means depend on the principle of jet constriction, where the jet issuing from a clear orifice will only fill part of the clear orifice cross-section. One suitable preferred throttling means is a diaphragm with the sharp edge in the direction of current flow, as shown in FIG. 1.

A further throttling means illustrating the same principle operates by admitting the protective medium tangentially into a cylindrical cavity. Because of the sharp deflection of the medium current in such a cylinder, and because of the centrifugal forces that do occur, the jet is constricted and a pressure reduction for a fairly large clear flow cross-section is achieved.

Further, so called spin throttles have proved useful, in which the medium current is not constricted, but wherein rather a strong rotational impulse is imparted to the flowing medium prior to its passing through the diaphragm cross-section. In this manner the flow through the cross-section is not normal but rather helical. Such a spin throttle consists of a cylindrical chamber with tangential entrance and axial exit operating as the restrictor. Thus, the pressure in such a spin throttle may be reduced from 10 atm. abs. at the entrance to 5 atm. abs. at the exit, the least diameter of the system being traversed by the current being for instance 6 mm at the entrance and the chamber diameter being 50 mm. As a comparison, a diaphragm diameter of 3 mm would be required for the same pressure reduction if a simple diaphragm were used.

In theory, there are no differences as concerns operating with liquid or gaseous protective media. But expenditures being less for subjecting liquids such as oil to high pressures, generally the pressure in the common protective medium will be selected as being of a higher value than for gases in order to achieve greater reliability and more even distribution to the individual tuyeres.

After termination of refining and upon tilting the converter, when there is no more melt above the tuyeres, the tuyeres are cooled with nitrogen or air. Furthermore, it is frequently desired in steel making to blow nitrogen transiently, for instance for 30 seconds. through the melt following termination of refining, for the purpose of diminshing the hydrogen content. In both cases, nitrogen or air is passed through the refining gas tube and through the annular slot between the two tubes of the tuyere (FIG. 1).

When using liquid hydrocarbons, for instance light fuel oil, as protective media, special measures must be taken so as to insure continuous switching from liquid to gaseous protecting medium. The residual quantity of the protecting medium in the lines should be as small as possible and should be rapidly removed. Liquids and gases cannot use the same throttling devices because the liquids have higher densities than the gases and therefore will flow at appreciably lower speeds in the supply lines. Therefore different cross-sections are required for the throttling devices for oil and gas. This necessity of alternating introduction of liquid and gaseous protecting media is provided for in the invention by providing separate supply lines for liquid and gaseous protecting media as far as the tuyeres, that is, as far as the converter bottom. These supply lines terminate into a common switching valve, from which each tuyere will be supplied either with a liquid or with a gaseous protective medium.

FIG. 2 shows a supply system for such protective media, allowing lossless switching from a liquid to gaseous protecting medium and vice versa.

A main 8 for gaseous protecting media, for instance hydrocarbons or nitrogen for cooling the tuyeres while the converter is tilted, is located near the converter mantle in the region of the tuyere entrances. Main 8 terminates in a 5/2 way switch valve 9. From there each tuyere is individually supplied with a liquid or a gaseous medium. Line 8 is permanently under pressure, even if during refining, a liquid protective medium is fed to the tuyeres.

A second main 10 for a liquid protective medium also terminates in switch valve 9. Main 10 is suitably installed for the purpose of protecting against high temperatures in a main 8 for the gaseous protecting medium or cooling gas. Main 10 is connected to a compression pump 11. Furthermore, a flow meter 12 is mounted in line 10, as is a three way valve 13 to relieve pressure from line 10 in the blocked state. The switch valve 9 is a 5/2 way valve controlled by the pressure of the liquid and gaseous protecting media. If the liquid pressure at the valve is larger than the pressure of the gaseous protecting medium, the valve will allow the liquid protecting medium to flow to the tuyeres while shutting off the gaseous protecting medium and simultaneously exhausting the lines between back pressure valve 14 and switch valve 9. If the pressure in line 10 falls below that in line 8, operation is reversed and the gaseous protective medium or cooling gas will be supplied to the tuyere. In this case the line segment between the switch valve 9 and back pressure valve 15 will be exhausted into the ambient. The liquid protective medium being at a higher pressure, for instance at 30 atm. abs., than is the gaseous protecting medium or cooling gas, which for instance may be at 10 atm. abs., switching on or off the oil pressure by means of valve 13 allows controlling the operation of switch valve 9.

Initially there are two lines, one for liquid, another for gaseous protecting media, leading from this control valve 9 and consolidated after back pressure valves 14 and 15 into a feed line for each tuyere. Throttles 16 and 17, corresponding to the particular media, are mounted in the line segments for gaseous and liquid protecting media between valve 9 and back pressure valves 14 and All lines should be as small and accessible as possible, and should be provided with a minimum of control devices. From this viewpoint, one may omit throttle 16 and so dimension the common protective media supply line for each tuyere that it will act as a throttle, that is, as a pressure loss line. Because of the smaller flow rates of liquid protective media, this line will not cause addi-' tional pressure losses, hence throttle 17 will be required in every case. i I

If a liquid protecting medium is being used during refining and a gas, for instance nitrogen, will only be used during converter tilting for the purpose of tuyere cooling, the device will operate as follows:

For tilted converter, the control valve 9 will switch in such manner that the cooling gas flows to the tuyere via back pressure valve 14. The second path of the valve 9 then leads into ambient through exhaust action. This ensures that no cooling gas may penetrate into oil line 10. Any possible leakage current would be driven into ambient via back pressure valve 15. The moment refining begins, line for the liquid protective medium will be put under pressure; this pressure being higher than that of the cooling gas, valve 9 will switch. Then the path of the liquid protecting medium via throttle l7 and via back pressure valve to the tuyere will .be'

clear. Simultaneously the line between back pressure valve 14 and control valve 9 will be exhausted into ambient. This excludes the feasibility of forcing liquid protecting medium into the cooling gas line. Any possible leakages in the back pressure valves may be immediately noticed by observing the exhaust orifices at control valve 9. The line from back pressure valves 14 and 15 to the tuyere is short and may be rapidly evacuated as regards residues of the liquid protecting medium following switching from the liquid to the gaseous protecting medium. a

FIG. 3 shows a section through a control valve 9. This valve is provided with an entry port 21 for liquid protective medium and an entry port for gaseous protecting medium or cooling gas and withone exit each for both media for each tuyere. Identical control valves are provided for each tuyere. The illustrated valve holds the advantage that only small volumes ofpreviously used protecting medium need be exhausted following switching. Operation of the control valve will be explained again below.

Both protecting media flow towards the valve body in axial direction, for instance the liquid'protective medium through entrance 21. There are twopositions for piston valve 22. In one switch position, it connects the liquid protective medium line with the radial exhausts 23, the numbers of which are determined by the numbers of the tuyeres, that is, with the supply lines to the individual tuyeres. Simultaneously, the radial exhausts 24 of the shut off supply line 21 for the gaseous protective medium or cooling gas are connected with one or more evacuation orifices. This switching position is shown in FIG. 3 and corresponds to the condition in which pressure of the liquid protective medium is higher than the pressure of the gaseous protective medium. If now the pressure of the liquid protective medium were to fall to zero, the piston valve will move into a second position and the control valve operation correspondingly will be reversed. FIG. 4 shows another embodiment of a control valve suitable in the practice of this invention.

The principle of pressure switching also applies to this control valve. The gaseous protective medium flows towards switch valve 30 via supply line 31, through a dirt filter 32 and through the axial valve opening 29. The liquid protective medium is supplied by line 34 through valve entrance 35 into valve chamber 36. There is a supply line 37 for every tuyere from this valve chamber 36. Corresponding to piston valve 22 of FIG. 3, a piston 38, which in this instance has been specifically shaped as a sphere, freely slides in valve chamber 36. The sphere 38 is shown in its first position, that is, for a lasting oil pressure which is always greater than the gaseous pressure, as in the preceding example, against seal 33; in its second position for shut off oil pressure, the sphere will be against seal 40.

According to the position of the switch, the outflow cross-section 41 for liquid and gaseous protecting media will be set differently. In the second switch position, that is, when operating with a gaseous protecting medium or with a cooling gas, seal 40 forms the stop for the valve piston, in this instance the sphere, and the entire cross-section 41 is cleared. This cross section then represents the desired restrictor. In the first switch position as shown in FIG. 4, that is, when there is oil pressure, the sphere will be pushing against stop 39 and the outflow cross-section 41 of the protecting medium will be only partlyuncovered. The clear cross-section is so designed that it forms the desired restrictor for the liquid protecting medium.

The following example demonstrates the effectiveness of the invention for even distribution and for alternating supply of liquid and gaseous protecting media to the refining gas tuyeres in a converter: v

' A converter of 40 tons capacity with eight refining gas tuyeres was used, where the inner diameter of the oxygen injection tube was 18 mm. Blowing was performed using an oxygen pressure of 20 atm. abs. Natural gas was used as the protecting medium and at a pressure of IO atm. abs. and in a ratio of 7 percent by volume with respect to the oxygen flow'rate. Initially the throttles of the invention were not used in the protecting medium supply lines to the individual tuyeres. Accordingly, the tuyeres evidenced very different burn-offs during operation. Deep craters were formed for some, whereas others projected from the bottom masonry.

Because of the strongly varying tuyere burn-offs, an average bottom life of about melts could be achieved.

Following installation of the throttling organs of the invention, in this instance diaphragms with a clear diameter of 3.8 mm, wear behavior of the converter bottom changed immediately. There were no longer individual tuyeres burning back, that is, there was no crater formation; also, there were no longer any tuyere stumps projecting above the bottom masonry. Mean life of converter bottoms was increased to approximately 200 melts.

In another campaign when propane was used as the protecting gas for the refining gas tuyeres, similar improved results were obtained. The proportion of propane with respect to oxygen flow rate was about 4 percent by volume. lnital pressure in the propane supply line was 4 atm. abs. in order to prevent liquefaction on account of the ordinary average seasonal temperatures. As propane pressure is increased, the boiling point rises, that is, there is an increase in the condensation temperature of propane to a temperature above the seasonal ambient. Thus for propane, the boiling point for 10 atm. abs. is about 30C.

In order to more fully achieve an even distribution of the protecting medium according to the invention, the propane pressure in the supply line was raised to 10 atm. abs. and the line simultaneously was provided with a heating device. Either steam or electrical heat may be used in combination with regulating devices for maintaining the propane supply lineat a temperature of 80C. These measures achieved the same improved bottom life as when natural gas was used as the protective medium.

We claim:

1. A process for the even distribution and supply of protective media to refining gas tuyeres in a converter, wherein the individual tuyeres consist of two concentric tubes, refining gas, being passed through the central one of the tubes and a liquid or gaseous protective medium being supplied through the annular space between the two tubes, wherein the improvement comprises providing the protective medium from a supply at super atmospheric pressure and lowering the pressure of said protective medium by at least two atmospheres absolute pressure prior to entry of said medium into the tuyeres, said pressure being lowered by means of throttling devices to approximately half the pressure at which said medium is supplied.

2. A process according to claim 1 wherein the throttles effect the desired pressure decrease by accelerating the protecting medium.

3. A process according to claim 1 wherein that the throttling devices are diaphragms.

4. A process according to claim 1 wherein the throttling devices include a constriction in the throttles whereby the effective jet cross-section is appreciably smaller than the orifice cross-section.

5. A process according to claim 1 wherein the throttling device causes the jet leaving the throttle to be provided with a spin.

6. A process according to claim 1 wherein liquid and gaseous protective media are used alternately.

7. A process according to claim 6 wherein the switching from liquid to gaseous protective medium or vice versa is effected by changing the pressure of one of the protective media.

8. The process of claim 1 in which the refining gas is oxygen.

' QRM PO-1OSO (10-69) "Eisenwerk UNITED STATES PATENT OFFICE QETIFICATE 0F CORRECTION Patent No. 3,852,() :2 Dated "December E 197 lnventofls) Helmut finuppel; harl Brotzmann; rians Georg; Fassbinder It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Gesellschaft Maximilianshutte V1.3 .I'Ifishould be --Eisenwerk-Gesellsohaf't Maximilianshutte rabid-- Rosenberg, Germany should be--Sulzbach-Rosenber;3, Germany-- Signzd and Sealed this A ttest:

RUTH C. MASON Arresting Officer C. MARSHALL DANN ('mnmissiuner uflalcnts and Trademarkx USCOMM-DC 5037G-P59 U S. GOVERNMENT PRINTING OFFICE: 1969 0-365-334, 

1. A PROCESS FOR THE EVEN DISTRIBUTION AND SUPPLY OF PROTECTIVE MEDIA TO REFINING GAS TUYERES IN A CONVERTER, WHEREIN THE INDIVIDUAL TUYERES CONSIST OF TWO CONCENTRIC TUBES, REFINING GAS, BEING PASSED THROUGH THE CENTRAL ONE OF THE TUBES AND A LIQUID OR GASEOUS PROTECTIVE MEDIUM BEING SUPPLIED THROUGH THE ANNULAR SPACE BETWEEN THE TWO TUBES, WHEREIN THE IMPROVEMENT COMPRISES PROVIDING THE PROTECTIVE MEDIUM FROM A SUPPLY AT SUPER ATMOSPHERIC PRESSURE AND LOWERING THE PRESSURE OF SAID PROTECTIVE MEDIUM BY AT LEAST TWO ATMOSPHERE ABSOLUTE PRESSURE PRIOR TO ENTRY OF SAID MEDIUM INTO THE TUYERES, SAID PRESSURE BEING LOWERED BY MEANS OF THROTTLING DEVICES TO APPROXIMATELY HALF THE PRESSURE AT WHICH SAID MEDIUM IS SUPPLIED.
 2. A process according to claim 1 wherein the throttles effect the desired pressure decrease by accelerating the protecting medium.
 3. A process according to claim 1 wherein that the throttling devices are diaphragms.
 4. A proceSs according to claim 1 wherein the throttling devices include a constriction in the throttles whereby the effective jet cross-section is appreciably smaller than the orifice cross-section.
 5. A process according to claim 1 wherein the throttling device causes the jet leaving the throttle to be provided with a spin.
 6. A process according to claim 1 wherein liquid and gaseous protective media are used alternately.
 7. A process according to claim 6 wherein the switching from liquid to gaseous protective medium or vice versa is effected by changing the pressure of one of the protective media.
 8. The process of claim 1 in which the refining gas is oxygen. 